(CNN) -- South Carolina Gov. Mark Sanford, already under fire for an extramarital relationship, should be impeached for abusing state finances, a Republican state senator said Monday.

A Republican senator in South Carolina says Gov. Mark Sanford should be impeached over financial violations.

Sen. David Thomas -- the chairman of the Senate constitutional and administrative subcommittee -- wrote to leaders of the Republican-controlled Senate, accusing the governor of violating state regulations.

The allegations involve flights he took to London, England, and China in 2006 and 2007 on state business. South Carolina requires the governor to charge the state the lowest rate available unless there are overriding circumstances, such as emergency travel.

"The two flights by Gov. Sanford were in violation of the South Carolina Code of Regulations," Thomas said in his letter. "The difference in price between the most economical and the more expensive price of the seats the governor chose is approximately $13,700."

Thomas said he thought the violations were enough to trigger impeachment proceedings.

"If I were in the House, the answer would be yes, I would be involved in the beginning of the impeachment process," he said. "I think there is enough data right now to take seriously a move toward impeachment. Is that sufficient for impeachment? That I don't know."

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Sanford has been under fire since he disappeared in late June. Initially, there was speculation that he had simply gone off to recover from a bruising legislative session, in which he lost a fight to reject $700 million in federal stimulus money. His office tried to quiet the rumors, saying Sanford was hiking along the Appalachian Trail.

But the governor offered a different account when spotted in the Atlanta, Georgia, airport after nearly a week out of pocket. With his wife nowhere in sight, a teary-eyed Sanford confessed to the affair with a woman from Argentina in a rambling news conference. He stepped down as head of the Republican governors' group.

Thomas urged Sanford to resign after he admitted his affair.

Sanford said then that he intended to continue as governor and would try to rebuild his relationship with his wife and family.

Last Friday, South Carolina first lady Jenny Sanford said she and her four boys were moving out of the governor's mansion in Columbia and back to their home in Charleston for the upcoming school year.

Jenny Sanford announced the news in a statement e-mailed to reporters, days after the family returned from a two-week vacation to an undisclosed location in Europe.

In response to his wife's decision, Sanford said, "The first lady's office has already put out a statement that speaks for the family, on this decision that we felt best, both for our process of reconciliation, and for the boys in the upcoming school year."